1. Field of the Invention
The present invention relates to a fiber optical fiber draw furnace for drawing optical fiber from a preform.
2. Description of Related Art
Known fiber optic draw furnaces control the draw of the optical fiber from the preform by monitoring various parameters, including among others fiber tension, fiber diameter, fiber velocity and furnace temperature. For example, see U.S. Pat. Nos. 5,0 79,433; 5,228,893 and 5,316,562.
Existing graphite resistance fiber optic draw furnace control methods utilize temperature feedback based on optical measurement using a pyrometer to control furnace temperature. The pyrometer requires a sight xe2x80x9cportxe2x80x9d that is essentially a cylindrical hole through the insulation material.
The use of the sight port results in several disadvantages including among other things uneven heating of the preform (temperature profile not uniform due to heat sink created by pyrometer port), accelerated graphite erosion (heating element, furnace insulation, etc.), and improper alignment and calibration of the pyrometer for proper furnace control feedback. Induced stresses created by a non-uniform thermal profile can result in optical and physical defects in the drawn fiber such as elevated attenuation loss, fiber curl, etc.
Another disadvantage of using a site port is that it will darken over time due to the frequent condensation of material on the transparent wall which blocks the light flux to be measured, as described in U.S. Pat. No. 4,317,666, column 1, lines 36-43.
Yet another disadvantage is that induced stresses are created by the non-uniform thermal profile of the preform which result in optical and physical defects in the drawn fiber such as elevated attenuation loss and fiber curl.
The present invention provides a fiber optic draw furnace having a fiber optic heating and draw control system that controls the heating of a fiber optic preform which is partially melted by a furnace and the drawing of an optical fiber from the fiber optic preform by a fiber drawing device.
The fiber optic heating and draw control system features a fiber optic heating and drawing device controller that responds to a furnace power consumption control signal from a fiber optic preform heating device in the furnace, for providing a furnace heating control signal to the fiber optic preform heating device in the furnace and a fiber tension draw control signal to the fiber drawing device to maintain a desired fiber draw tension on the optical fiber.
In one embodiment, the fiber optic heating and drawing device controller is a programmable logic controller.
The fiber optic preform heating feedback signal from the fiber optic preform heating device is a furnace power consumption feedback signal that feeds information about the power consumption of the furnace back to the fiber optic preform heating and fiber drawing controller.
The furnace power consumption feedback signal includes information about a sensed measurement of voltage and amperage of electrical energy used to heat the furnace.
One advantage of the present invention is that it eliminates the need for an optical pyrometer port, which results in a symmetrical temperature profile around the circumference of the preform and also helps eliminate induced stresses that can cause defects in an optical fiber.
Another advantage is that the overal furnace life is increased, reducing operating costs, because graphite erosion is reduced. Reducing graphite erosion results in a cleaner furnace (dramatically reduces graphite dust and particulate generation) and increased furnace stability and longevity. This results in a cleaner furnace having significantly less graphite dust and particulate generation while increasing furnace stability and longevity. A clean furnace is essential for the manufacturing of high strength optical fiber.
The present invention may be more clearly understood from the following description of a specific and preferred embodiment read in conjunction with the accompanying detailed drawing.